Had time to look at this issue more closely, this is how the program behaves:
Correct, the General Ledger Trial Balance Report presents correctly the negative bank account balance as Credit Amount (and not as Debit Amount). My problem is not related to this report.
On the Balance Sheet Report this "transfer" of a negative bank account balance does not take place from Total Assets "side" to Total Liabilities & Capital "side".
This created an easy to spot error: On my Balance Sheet both the "Total Assets" and "Total Liabilities & Capital" amounts were negative, say -1000, and the correct amount for both was positive, say +10000. - One glimpse by a qualified accountant and I had a lot explaining to do
I will discuss this more later with an accountant.